Balanced discharge method for energy storage units and distributed energy storage system
By acquiring the current charge and expected discharge time of the energy storage unit, calculating and broadcasting the discharge current, balanced discharge of the distributed energy storage system is achieved, solving the problem of battery charge imbalance, protecting battery life and improving system efficiency.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- CHONGQING YUXIN MICRO INFORMATION TECH CO LTD
- Filing Date
- 2025-12-15
- Publication Date
- 2026-04-14
AI Technical Summary
In distributed energy storage systems, how can we maximize discharge capacity under complex parallel and series topologies and battery power imbalance conditions, while protecting individual batteries from over-discharge and avoiding affecting battery life?
By acquiring the current power of each energy storage unit in each string, calculating the discharge current of each string based on the preset expected discharge time and current power, and broadcasting the discharge time and current to the corresponding strings and energy storage units, each unit calculates its own discharge voltage based on its own power and string current, ensuring that it discharges synchronously within the expected time, and using a wireless communication module for real-time coordination and control.
It achieves stable and balanced discharge of the energy storage system, maximizes battery life and charge/discharge capacity utilization, and ensures efficient system operation.
Smart Images
Figure CN121863607A_ABST
Abstract
Description
Technical Field
[0001] This invention relates to the field of photovoltaic energy storage technology, and in particular to a method for equalizing the discharge of energy storage units and a distributed energy storage system. Background Technology
[0002] In battery management systems, it is crucial to ensure that each battery in a distributed energy storage system achieves balanced charging to maximize capacity and balanced discharging during system discharge. The lifespan of batteries in a distributed energy storage system is affected by ambient temperature, charging / discharging current, voltage, and the number of charge / discharge cycles. Different charge / discharge measurements have a significant impact on battery health, lifespan, and total effective discharge capacity.
[0003] In distributed energy storage systems deployed under photovoltaic panels or other configurations, it is of great significance to manage distributed energy storage units to achieve stable and balanced discharge of multiple strings connected in parallel under different inverters and multiple batteries connected in series within strings, under conditions of limited communication and control, so as to achieve optimal battery life management and maximize the total effective discharge capacity.
[0004] Therefore, overcoming the shortcomings of the existing technology is an urgent problem to be solved in this technical field. Summary of the Invention
[0005] The technical problem to be solved by this invention is how to maximize the discharge capacity of a distributed energy storage system under the conditions of complex parallel and series topologies and unbalanced battery power, while protecting individual batteries from over-discharge and avoiding affecting battery life.
[0006] The present invention adopts the following technical solution: Firstly, a method for equalizing the discharge of an energy storage unit is provided, including: Get the current power level of each energy storage unit in each string; The discharge current of each string is obtained based on the preset expected discharge time and the current charge of each energy storage unit. The expected discharge time and the corresponding discharge current are broadcast to the respective strings and energy storage units respectively; Each energy storage unit obtains its own discharge voltage based on its current power, expected discharge time, and discharge current of the string it belongs to, and then discharges synchronously within the expected discharge time according to its own discharge voltage.
[0007] Preferably, obtaining the current power of each energy storage unit in each string specifically includes: The energy storage unit periodically collects and calculates its current power level based on its built-in power management module; The data packet containing its unique identifier and current power level is sent to the central controller via a wireless communication network through the wireless communication module integrated in the energy storage unit. Each energy storage unit's unique identifier includes its own inverter number, string number, and energy storage unit number.
[0008] Preferably, the step of obtaining the discharge current of each string based on the preset expected discharge time and the current charge of each energy storage unit includes: The total power of each string and the total power of the system are obtained based on the current power of each energy storage unit. The total system discharge power is obtained based on the total system charge and the expected discharge time. Based on the proportion of the total power of each string to the total power of the system, the total discharge power of the system is allocated to each string to obtain the discharge power of each string. The discharge current of each string is obtained based on the discharge power of each string.
[0009] Preferably, the step of obtaining the discharge current of each string based on the preset expected discharge time and the current charge of each energy storage unit specifically includes: By summing up the current electricity reported by all energy storage units at the current moment, the total electricity of the distributed energy storage system at the current moment can be obtained. Divide the total system power by the expected discharge time to obtain the total system discharge power; The total power of each string is calculated by summing the current power reported by all energy storage units in each string. The discharge power ratio of each string is allocated according to the proportion of the total power of each string to the total power of the system. The discharge power of each string is obtained according to the discharge power ratio. Based on the allowable operating voltage range of the Maximum Power Point Tracking (MPPT) interface, a DC bus reference voltage is set for one or more strings connected in parallel to the same MPPT interface, and the discharge current of each string is obtained according to the discharge power of each string and the DC bus reference voltage.
[0010] Preferably, broadcasting the expected discharge time and the corresponding discharge current to the respective strings and energy storage units specifically includes: The central controller generates multiple downlink control command frames, each containing the expected discharge time and, for at least one target string, including its calculated discharge current. The central controller uses wireless multicast or broadcast communication to send downlink control command frames to all energy storage units in the target string. In the multicast method, the communication address of the string is used as the target address.
[0011] Preferably, each energy storage unit obtains its own discharge voltage based on its current power level, expected discharge time, and discharge current of the string it belongs to, specifically including: Each energy storage unit calculates the discharge energy it needs to release based on its current power, expected discharge time, and discharge current of the string it belongs to, and then calculates the target average discharge power. The self-discharge voltage that each energy storage unit needs to maintain during the discharge process is obtained based on the target average discharge power and the discharge current of the string.
[0012] Preferably, the method further includes: During the discharge process, each energy storage unit samples its actual output current in real time and compares the actual output current with the discharge current of its string. If there is a deviation between the actual output current and the discharge current of the string, the output voltage reference value of the DC-DC converter is dynamically adjusted through a preset control algorithm. The output voltage is increased or decreased to compensate for the current fluctuation, so that the actual output current stably tracks the discharge current of the string.
[0013] Preferably, the method further includes: During the discharge process, if any energy storage unit detects that the voltage of its own battery module reaches or falls below the preset discharge cutoff voltage threshold, or the current charge level is below the safety threshold, it will ignore the downlink control command frame sent by the central controller, reduce the discharge current to zero or discharge with the minimum safe current, and report alarm information to the central controller through the wireless communication network. Upon receiving an alarm message or detecting an abnormal decrease in the total system discharge power, the central controller regenerates and sends out a new downlink control command frame.
[0014] Preferably, the method further includes broadcasting the expected discharge time and the corresponding discharge current to the corresponding string and energy storage unit via WIoTa (Wide-range Internet Of Things communication protocol), NB-IoT (Narrowband IoT), or LORA (Long Range).
[0015] In a second aspect, a distributed energy storage system is provided for realizing the method of balanced discharge of energy storage units as described in the first aspect, the distributed energy storage system comprising: A central controller, equipped with a processor, memory and wireless communication interface; Multiple energy storage units, each energy storage unit including at least a battery module, a DC-DC converter, a power management module and a wireless communication module; Multiple energy storage units are connected in series to form a string, and one or more strings are connected in parallel to the DC input terminal of an inverter.
[0016] Compared with the prior art, the beneficial effects of the present invention are as follows: This invention obtains the current power level of each energy storage unit in each string; calculates the discharge current of each string based on a preset expected discharge time and the current power level of each energy storage unit; broadcasts the expected discharge time and corresponding discharge current to the corresponding strings and energy storage units; each energy storage unit calculates its own discharge voltage based on its current power level, expected discharge time, and the discharge current of its string, and synchronously discharges within the expected discharge time according to its own discharge voltage; this invention calculates the optimal discharge strategy by periodically reporting the current power level of the energy storage units, and achieves real-time coordinated control of the discharge voltage and discharge current of energy storage units in different inverters and strings through a simplified wireless communication method, thereby maximizing battery life and charge / discharge capacity utilization, and realizing the stable and efficient operation of the distributed energy storage system. Attached Figure Description
[0017] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.
[0018] Figure 1 This is a schematic diagram of the structure of a distributed energy storage system provided in an embodiment of the present invention; Figure 2 This is a flowchart illustrating a method for equalizing discharge of an energy storage unit according to an embodiment of the present invention; Figure 2a This is a signaling schematic diagram of a method for equalizing discharge of an energy storage unit provided in an embodiment of the present invention; Figure 3 This is a schematic diagram of a process for obtaining the current power of an energy storage unit according to an embodiment of the present invention; Figure 4 This is a schematic diagram of a process for obtaining the discharge current of each string according to an embodiment of the present invention; Figure 5This is a schematic diagram of a process for obtaining the self-discharge voltage of each energy storage unit according to an embodiment of the present invention; Figure 6 This is another flowchart illustrating a method for equalizing discharge of an energy storage unit provided in an embodiment of the present invention; Figure 7 This is a schematic diagram of a process for achieving balanced discharge after a failure of an energy storage unit, provided by an embodiment of the present invention. Detailed Implementation
[0019] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the invention.
[0020] Unless the context otherwise requires, throughout the specification and claims, the term "comprising" is interpreted as openly inclusive, meaning "including, but not limited to." In the description of the specification, terms such as "one embodiment," "some embodiments," "exemplary embodiment," "example," "specific example," or "some examples" are intended to indicate that a particular feature, structure, material, or characteristic associated with that embodiment or example is included in at least one embodiment or example of this disclosure. The illustrative representations of the above terms do not necessarily refer to the same embodiment or example. Furthermore, the specific features, structures, materials, or characteristics mentioned may be included in any suitable manner in any one or more embodiments or examples; that is, although they may be incorporated into embodiments or examples using the above terms for reasons such as order and position, it does not limit them to be incorporated in combination by a single embodiment or example.
[0021] In the description of this invention, the terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of indicated technical features. Thus, a feature defined with "first" or "second" may explicitly or implicitly include one or more of that feature. In the description of embodiments of this disclosure, unless otherwise stated, "a plurality of" means two or more. Furthermore, for example, the description may use the prefix "A" or "B" to describe the same type of nouns as two independent entities. In this case, the corresponding features defined with "A" and "B" are used only to distinguish between similar entities and should not be construed as indicating or implying relative importance or implicitly specifying the number of indicated technical features.
[0022] In describing some embodiments, the terms "coupled," "coupled," and "connected," and their derivative expressions, may be used. For example, the term "connected" may be used in describing some embodiments to indicate that two or more components have direct physical or electrical contact with each other. Similarly, the term "coupled" may be used in describing some embodiments to indicate that two or more components have direct physical or electrical contact. However, the terms "connected" or "coupled" may also refer to two or more components that do not have direct contact with each other but still cooperate or interact with each other, such as "optical coupling," "wireless connection," etc. The embodiments disclosed herein are not necessarily limited to the scope of this invention.
[0023] Furthermore, the technical features involved in the various embodiments of the present invention described below can be combined with each other as long as they do not conflict with each other.
[0024] Example 1: To provide a detailed explanation of the method for equalizing the discharge of energy storage units proposed in this invention, this embodiment first introduces a distributed energy storage system. In one embodiment, such as... Figure 1 As shown, the distributed energy storage system includes: a central controller equipped with a processor (not shown), a memory (not shown), and a wireless communication interface (not shown); multiple energy storage units, each energy storage unit including at least a battery module (not shown), a DC-DC converter (not shown), a power management module (not shown), and a wireless communication module (not shown); wherein, the multiple energy storage units are connected in series to form a string, and one or more strings are connected in parallel to the DC input terminal of an inverter.
[0025] The central controller performs core calculations, formulates discharge strategies, and issues control commands. Its processor performs calculations (such as calculating total power, allocating power, and determining current). The memory stores power data, historical data, and system parameters reported by each energy storage unit. The wireless communication interface receives data reported by all energy storage units and broadcasts corresponding control commands.
[0026] The battery module in the energy storage unit is the core energy storage carrier, used to store electrical energy. The DC-DC converter enables each energy storage unit to independently and flexibly adjust its output voltage and current. The power management module is used to monitor the state of charge in the battery module in real time and detect the current power level. The wireless communication module is used to report the status of each energy storage unit (such as the current power level) and receive control commands (discharge time, discharge current, etc.) from the central controller.
[0027] In one embodiment, in the distributed energy storage system, multiple energy storage units and photovoltaic panels are connected in parallel, and then connected in series (typically 20-30 energy storage units per group) to form a string. Multiple strings are connected to the DC input ports of an inverter. A typical string inverter usually includes 8-30 DC input ports, sharing 4-6 MPPTs (Multi-Level Photovoltaics). The DC input ports of the same MPPT are connected in parallel. The input voltage of the string inverter is generally 1000-1500V, and the output is 800V AC. The 800V AC outputs of multiple string inverters are connected to a transformer substation, which transforms the voltage to 10kV or 30kV.
[0028] Example 2: Based on the distributed energy storage system proposed in Embodiment 1, this embodiment proposes a method for equalizing the discharge of energy storage units. In one embodiment, such as... Figure 2 and Figure 2a As shown, the method includes: Step 101: Obtain the current power of each energy storage unit in each string.
[0029] Specifically, the central controller obtains real-time battery state-of-charge information (i.e., current battery level) for each energy storage unit in each string under its jurisdiction.
[0030] Step 102: Obtain the discharge current of each string according to the preset expected discharge time and the current charge of each energy storage unit.
[0031] The central controller performs discharge strategy optimization calculations based on a preset expected discharge time and the current power obtained from all energy storage units, and calculates a specified discharge current for each string. The specific calculation method will be explained below.
[0032] Step 103: Broadcast the expected discharge time and the corresponding discharge current to the respective strings and energy storage units.
[0033] The central controller transmits the expected discharge time and the calculated discharge current for each string to the corresponding string and all its energy storage units via a wireless communication network. In one embodiment, the central controller generates multiple downlink control command frames, each containing the expected discharge time and, for at least one target string, its calculated discharge current. The central controller uses wireless multicast or broadcast communication to send the downlink control command frames to all energy storage units within the target string, wherein the multicast method uses the string's communication address as the target address.
[0034] In one embodiment, the expected discharge time and the corresponding discharge current can be broadcast to the corresponding string and energy storage unit via WIoTa, NB-IoT, or LoRa.
[0035] The instructions issued by the central controller (i.e., downlink control instruction frames) can control one or more inverters in one instruction. They can use the same discharge start and end times, but different discharge voltages and discharge currents are required for different strings, thus realizing the separate control of strings in a multicast manner.
[0036] Step 104: Each energy storage unit obtains its own discharge voltage based on its current power, expected discharge time, and discharge current of the string it belongs to, and then discharges synchronously within the expected discharge time according to its own discharge voltage.
[0037] In this system, each energy storage unit, upon receiving the expected discharge time and the discharge current of its string, independently calculates the self-discharge voltage required to fully discharge its own charge within the expected discharge time based on its current charge level. It then uses closed-loop control of its own DC-DC converter to discharge at its own discharge voltage, ensuring that all energy storage units synchronously reach the discharge termination condition within the same expected discharge time. In one embodiment, the discharge termination condition for all energy storage units can be detecting a current charge level of 0 or a current charge level below a preset value (e.g., 5% of full load charge).
[0038] In one embodiment, such as Figure 3 As shown, obtaining the current power of each energy storage unit in each string specifically includes: Step 1011: The energy storage unit periodically collects and calculates its current power based on its built-in power management module.
[0039] Each energy storage unit's power management module synchronously collects raw data at a fixed sampling period (e.g., once every 5 seconds), including the battery module's terminal voltage, the charging and discharging current measured by a surface-mount precision shunt or Hall effect sensor, and readings from multiple temperature sensors distributed on the battery surface. After filtering the collected raw data, the system uses a built-in dedicated algorithm to calculate the state of charge (i.e., the current power level) in real time based on the collected raw data.
[0040] Step 1012: The data packet containing its own unique identifier and current power level is sent to the central controller via the wireless communication module integrated in the energy storage unit through the wireless communication network.
[0041] Each energy storage unit's unique identifier includes its own inverter number, string number, and energy storage unit number.
[0042] Among them, after obtaining the latest current power, the communication protocol stack is started, and the current timestamp, the verified current power, and its own unique identifier are jointly encapsulated into a data frame (i.e., a data packet) that conforms to a specific application layer protocol.
[0043] In one embodiment, the own unique identifier adopts a three-level cascaded structure, where the inverter number locates the maximum energy conversion unit of the distributed energy storage system, the string number locates a specific series circuit under the inverter, and the energy storage unit number finally accurately locates a specific individual energy storage unit in the string.
[0044] In one embodiment, for example, the own unique identifier INV-01-STR-02-U-15 points to the energy storage unit 15 of string 2 in inverter 1.
[0045] In order to obtain the discharge current of each string, in one embodiment, the method for obtaining the discharge current of each string according to the preset expected discharge time and the current power of each energy storage unit respectively includes: obtaining the total power of each string and the total system power according to the current power of each energy storage unit respectively; obtaining the total system discharge power according to the total system power and the expected discharge time; allocating the total system discharge power to each string according to the proportion of the total power of each string to the total system power, to obtain the discharge power of each string; obtaining the discharge current of each string according to the discharge power of each string.
[0046] In one embodiment, as Figure 4 shown, the method for obtaining the discharge current of each string according to the preset expected discharge time and the current power of each energy storage unit respectively specifically includes: Step 1021: Summarize the current powers reported by all energy storage units at the current moment to obtain the total system power of the distributed energy storage system at the current moment.
[0047] Among them, at the beginning of each control cycle, the central controller extracts the latest reported current powers of all energy storage units at the current moment from its real-time database (from the memory), and then performs a global summation operation to accumulate the current powers of all energy storage units, so as to obtain the total system power.
[0048] In one embodiment, for N strings under one inverter, each string has M photovoltaic panels and M energy storage units. For example, each energy storage unit regularly reports its current power C_n_m, where n represents the string number under the inverter, 0 < n ≤ N, N is the total number of strings; m represents the energy storage unit number on the string, 0 < m ≤ M, M is the total number of energy storage units on each string.
[0049] Then, the total system power at the current moment is C_total=Sum(C_n_m,n=1~N,m=1~M), where Sum is the summation operation.
[0050] Step 1022: Divide the total system power by the expected discharge time to obtain the total system discharge power.
[0051] In this process, after the central controller obtains the total system power C_total calculated in step 1021, it divides it by the preset expected discharge time. The total system discharge power W_out = C_total / T, where T is the expected discharge time. The calculation result represents the average output power that the entire distributed energy storage system cluster needs to maintain in order to achieve the goal of completely releasing the total energy of the distributed energy storage system within the expected discharge time.
[0052] Step 1023: Calculate the sum of the current power reported by all energy storage units in each string to obtain the total power of each string, and allocate the discharge power ratio to each string according to the ratio of the total power of each string to the total power of the system, and obtain the discharge power of each string according to the discharge power ratio.
[0053] In order to distribute the total system discharge power reasonably to each string, the central controller first needs to calculate the share that each string should bear. To do this, the central controller needs to sum the current power of all the energy storage units connected in series for each string to obtain the total power of each string. Then, it calculates the percentage of the total power of each string to the total power of the system. This percentage represents the weight of the string in the current system energy reserve. Finally, the central controller allocates the total system power according to this weight to obtain the discharge power allocated to each string.
[0054] The total power of each string is C_n_total = Sum(C_n_m, m = 1~M).
[0055] To achieve synchronous discharge, the discharge power of each string should be proportional to the total charge of that string. Therefore, the discharge power of each string is W_n_out = (C_n_total / C_total) × W_out.
[0056] Step 1024: Based on the allowable operating voltage range of the MPPT interface, set the DC bus reference voltage for one or more strings connected in parallel to the same MPPT interface, and obtain the discharge current of each string based on the discharge power of each string and the DC bus reference voltage.
[0057] Since the strings are connected in parallel to the MPPT interface, the controller must first set a unified DC bus reference voltage for all strings under the same MPPT interface. The selection of this DC bus reference voltage must be strictly limited to the optimal operating voltage range specified in the MPPT technical specifications. After determining the common DC bus reference voltage, for each string, the central controller can accurately calculate the discharge current that the string needs to maintain by using its allocated discharge power and the power calculation formula of Ohm's law. Finally, the calculated discharge current of each string will be sent to the string along with the expected discharge time, thereby accurately transmitting the central optimization decision to the execution end (i.e., each energy storage unit).
[0058] Where the discharge voltage of strings under the same MPPT interface is the same, assuming it is the DC bus reference voltage V_out, the final discharge current of different strings is I_out_n = W_n_out / V_out,0 <n≤N。
[0059] In one embodiment, such as Figure 5 As shown, each energy storage unit obtains its own discharge voltage based on its current power level, expected discharge time, and the discharge current of its string, specifically including: Step 1041: Each energy storage unit calculates the discharge energy it needs to release based on its current power, expected discharge time, and discharge current of the string it belongs to, and then calculates the target average discharge power.
[0060] Specifically, after each energy storage unit receives the expected discharge time and the discharge current of its string from the central controller via the wireless communication module, it first determines the total energy to be released during the entire discharge cycle based on the current charge C_n_m provided by its own battery management module. Then, by dividing the total energy to be released by the expected discharge time, the target average discharge power W_n_m = C_n_m / T that the energy storage unit needs to maintain during the entire discharge process can be obtained.
[0061] Step 1042: Based on the target average discharge power and the discharge current of the string, obtain the self-discharge voltage that each energy storage unit needs to maintain during the discharge process.
[0062] After obtaining the target average discharge power, the energy storage unit calculates its own discharge voltage V_out_n_m = W_n_m / I_out_n based on the received discharge current of its string. The calculated self-discharge voltage V_out_n_m is the target output voltage that the DC-DC converter of the energy storage unit needs to adjust to achieve during subsequent discharge.
[0063] Through the above calculations, each energy storage unit independently determines the voltage level it needs to contribute to achieve the global balanced discharge target of the system. Energy storage units with higher current charge will automatically calculate a higher self-discharge voltage to contribute more power, while energy storage units with lower current charge will calculate a lower self-discharge voltage, thereby achieving balanced discharge of all energy storage units under the same string current and the same discharge time.
[0064] To ensure the stability and accuracy of the distributed energy storage system during the discharge process, in one embodiment, such as Figure 6 As shown, the method further includes: Step 201: During the discharge process, each energy storage unit samples its actual output current in real time and compares the actual output current with the discharge current of the string it belongs to.
[0065] After the discharge command is executed, each energy storage unit enters a real-time monitoring and adjustment state. Specifically, each energy storage unit continuously samples the actual output current I_actual to the DC bus through a high-bandwidth current sensor at a fixed frequency (e.g., 10kHz) of its internal controller. This instantaneous measurement value is then compared with the discharge current I_n of the string to which it belongs, issued by the central controller, and the real-time current deviation ΔI=I_actual-I_n is calculated.
[0066] Step 202: If there is a deviation between the actual output current and the discharge current of the string, the output voltage reference value of the DC-DC converter is dynamically adjusted through a preset control algorithm. The current fluctuation is compensated by increasing or decreasing the output voltage, so that the actual output current stably tracks the discharge current of the string.
[0067] If the absolute value of the real-time current deviation ΔI exceeds the preset dead zone threshold, the energy storage unit immediately starts a preset control algorithm (e.g., proportional-integral control algorithm). This algorithm aims to eliminate the current deviation and dynamically and continuously adjusts the output voltage reference value of its DC-DC converter according to the magnitude and direction of the deviation.
[0068] The specific adjustment logic is as follows: if the actual output current is lower than the discharge current of its string (ΔI is negative), the output voltage reference value is increased according to the adjustment amount calculated by the control algorithm; otherwise, the output voltage reference value is decreased. Through this real-time adjustment, the energy storage unit can actively compensate for current disturbances caused by DC bus voltage fluctuations, line impedance differences, or slight changes in parameters of adjacent units, thereby forming a fast local negative feedback closed loop. This ensures that the actual output current of each energy storage unit can highly stably track the discharge current of its string, ultimately achieving stable and accurate system power output throughout the entire discharge process.
[0069] To prevent one or more energy storage units from malfunctioning and affecting the balanced discharge of the entire distributed energy storage system, in one embodiment, such as Figure 7 As shown, the method further includes: Step 301: During the discharge process, if any energy storage unit detects that the voltage of its own battery module reaches or falls below the preset discharge cutoff voltage threshold, or the current charge level is below the safety threshold, it will ignore the downlink control command frame sent by the central controller, reduce the discharge current to zero or discharge with the minimum safe current, and report alarm information to the central controller through the wireless communication network.
[0070] During the discharge process, the power management module of each energy storage unit continuously monitors key battery safety parameters in parallel with extremely high priority. These parameters primarily include whether the battery voltage reaches or falls below the discharge cutoff voltage threshold and whether the remaining charge is below a safety threshold (e.g., 5% of full load charge). Once any of these conditions is triggered, the local controller within the energy storage unit will immediately take action, ignoring instructions from the central controller and indicating that local safety protection has the highest authority. It will forcibly override the current control instructions from the central controller and perform operations including hard shutdown and soft derating.
[0071] Hard shutdown involves reducing the discharge current to zero, completely stopping the discharge; this is the safest measure. Soft derating involves discharging at the minimum safe current (a preset, extremely small current value). This protects the battery while potentially maintaining the system's weak output. Simultaneously with these protective actions, the energy storage unit sends a high-priority alarm message to the central controller via the wireless communication network. The alarm message should include the energy storage unit identifier, the reason for the protection trigger (e.g., low voltage), and the current status.
[0072] Step 302: After receiving an alarm message or detecting an abnormal decrease in the total system discharge power, the central controller regenerates a new downlink control command frame and sends it out.
[0073] The central controller can detect system anomalies in two ways: either by directly receiving alarm information reported by the units, or by monitoring the total system discharge power and detecting an unexplained abnormal drop in power (i.e., the actual power is significantly lower than the commanded power), thus inferring that a unit that did not report the anomaly may have failed or gone offline.
[0074] After confirming that the system status has changed, the central controller immediately re-executes the entire optimization calculation process (i.e., steps 101-104 above). During this calculation process, the power data (current power) of energy storage units that have triggered protection, are offline, or have failed will be excluded.
[0075] Based on the total power and string composition of the remaining normally operating energy storage units, the new total power, string power allocation, and discharge current of each string are recalculated, and new control commands are generated and sent to all energy storage units that are still operating normally.
[0076] In one embodiment, according to the above method, the distributed energy storage system will not experience operational abnormalities due to the failure of a single energy storage unit. It can quickly adjust its discharge strategy and continue to discharge in the optimal way under new constraints (i.e., fewer faulty energy storage units) until the balanced discharge ends, thereby achieving dynamic rebalancing of the distributed energy storage system.
[0077] In summary, this invention calculates the optimal discharge strategy by periodically reporting the current power of the energy storage units, and achieves real-time coordinated control of the discharge voltage and discharge current of energy storage units in different inverters and strings through a simplified wireless communication method. This maximizes battery life and charge / discharge capacity utilization, and enables the stable and efficient operation of the distributed energy storage system.
[0078] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of the present invention should be included within the protection scope of the present invention.
Claims
1. A method for equalizing discharge of an energy storage unit, characterized in that, include: Get the current power level of each energy storage unit in each string; The discharge current of each string is obtained based on the preset expected discharge time and the current charge of each energy storage unit. The expected discharge time and the corresponding discharge current are broadcast to the respective strings and energy storage units respectively; Each energy storage unit obtains its own discharge voltage based on its current power, expected discharge time, and discharge current of the string it belongs to, and then discharges synchronously within the expected discharge time according to its own discharge voltage.
2. The method for equalizing discharge of an energy storage unit according to claim 1, characterized in that, The step of obtaining the current power of each energy storage unit in each string specifically includes: The energy storage unit periodically collects and calculates its current power level based on its built-in power management module; The data packet containing its unique identifier and current power level is sent to the central controller via a wireless communication network through the wireless communication module integrated in the energy storage unit. Each energy storage unit's unique identifier includes its own inverter number, string number, and energy storage unit number.
3. The method for equalizing discharge of an energy storage unit according to claim 1, characterized in that, The step of obtaining the discharge current of each string based on the preset expected discharge time and the current charge of each energy storage unit includes: The total power of each string and the total power of the system are obtained based on the current power of each energy storage unit. The total system discharge power is obtained based on the total system charge and the expected discharge time. Based on the proportion of the total power of each string to the total power of the system, the total discharge power of the system is allocated to each string to obtain the discharge power of each string. The discharge current of each string is obtained based on the discharge power of each string.
4. The method for equalizing discharge of an energy storage unit according to claim 3, characterized in that, The step of obtaining the discharge current of each string based on the preset expected discharge time and the current charge of each energy storage unit specifically includes: By summing up the current electricity reported by all energy storage units at the current moment, the total electricity of the distributed energy storage system at the current moment can be obtained. Divide the total system power by the expected discharge time to obtain the total system discharge power; The total power of each string is calculated by summing the current power reported by all energy storage units in each string. The discharge power ratio of each string is allocated according to the proportion of the total power of each string to the total power of the system. The discharge power of each string is obtained according to the discharge power ratio. Based on the allowable operating voltage range of the MPPT interface, a DC bus reference voltage is set for one or more strings connected in parallel to the same MPPT interface, and the discharge current of each string is obtained according to the discharge power of each string and the DC bus reference voltage.
5. The method for equalizing discharge of an energy storage unit according to claim 1, characterized in that, The broadcasting of the expected discharge time and corresponding discharge current to the respective strings and energy storage units specifically includes: The central controller generates multiple downlink control command frames, each containing the expected discharge time and, for at least one target string, including its calculated discharge current. The central controller uses wireless multicast or broadcast communication to send downlink control command frames to all energy storage units in the target string. In the multicast method, the communication address of the string is used as the target address.
6. The method for equalizing discharge of an energy storage unit according to claim 1, characterized in that, Each energy storage unit obtains its own discharge voltage based on its current power level, expected discharge time, and the discharge current of its string, specifically including: Each energy storage unit calculates the discharge energy it needs to release based on its current power, expected discharge time, and discharge current of the string it belongs to, and then calculates the target average discharge power. The self-discharge voltage that each energy storage unit needs to maintain during the discharge process is obtained based on the target average discharge power and the discharge current of the string.
7. The method for equalizing discharge of an energy storage unit according to claim 1, characterized in that, The method further includes: During the discharge process, each energy storage unit samples its actual output current in real time and compares the actual output current with the discharge current of its string. If there is a deviation between the actual output current and the discharge current of the string, the output voltage reference value of the DC-DC converter is dynamically adjusted through a preset control algorithm. The output voltage is increased or decreased to compensate for the current fluctuation, so that the actual output current stably tracks the discharge current of the string.
8. The method for equalizing discharge of an energy storage unit according to claim 1, characterized in that, The method further includes: During the discharge process, if any energy storage unit detects that the voltage of its own battery module reaches or falls below the preset discharge cutoff voltage threshold, or the current charge level is below the safety threshold, it will ignore the downlink control command frame sent by the central controller, reduce the discharge current to zero or discharge with the minimum safe current, and report alarm information to the central controller through the wireless communication network. Upon receiving an alarm message or detecting an abnormal decrease in the total system discharge power, the central controller regenerates and sends out a new downlink control command frame.
9. The method for equalizing discharge of an energy storage unit according to claim 1, characterized in that, The method further includes broadcasting the expected discharge time and the corresponding discharge current to the corresponding string and energy storage unit via WIoTa, NB-IoT or LoRa.
10. A distributed energy storage system, characterized in that, A method for achieving balanced discharge of energy storage units as described in any one of claims 1-9, wherein the distributed energy storage system comprises: A central controller, equipped with a processor, memory and wireless communication interface; Multiple energy storage units, each energy storage unit including at least a battery module, a DC-DC converter, a power management module and a wireless communication module; Multiple energy storage units are connected in series to form a string, and one or more strings are connected in parallel to the DC input terminal of an inverter.